1. Field of the Invention
This invention relates to a process for producing improved particulate resole resins, as well as to the resins so produced.
2. Description of the Prior Art
U.S. Pat. No. 4,206,095 (Wynstra et al.) describes a process for the production of particulate solid, heat-reactive, substantially water-insoluble resoles. The process comprises the steps of: (a) reacting formaldehyde, a phenol, and hexamethylenetetramine or a compound containing amino hydrogen, in an aqueous medium containing an effective amount of certain protective colloids, for a period of time and at a temperature sufficient to produce an aqueous dispersion of a particulate solid, heat-reactive, substantially water-insoluble thermosetting resole; and (b) recovering the particulate resole from the aqueous dispersion.
These resole resins, however, because of chemical composition boundaries, have a limited range of reactivity as is well known to those skilled in the art. Extensive analysis, using AMOE molding evaluations as well as dynamic mechanical analysis, shows that the cure rate of these resoles is slower than that of many other known resole and novolac resins. This slower cure rate limits the use of these resole products in such applications as molding compound resins and wafer board. A rapid cure rate is especially important in wafer board manufacture where cycle times are commercially critical. Another property of these resoles for which improvement is desirable is their sinter resistance. The fiber bonding product produced using these resoles has exhibited sinter resistance inferior to pulverized two-step resins. The sinter resistance is controlled primarily by the glass transition temperature (hereinafter referred to as "T.sub.g ") of the resole resin. Increasing the T.sub.g of these resoles from 5.degree. to 15.degree. C. would improve the sinter resistance to the point where they would be comparable to novolac resin intermediates having high sinter resistance.
It would, therefore, be desirable to develop a particulate resole resin having an improved cure rate and sinter resistance so that particulate resoles could be applied in those areas where such properties are required.